This invention relates to bending heat-softenable sheet material and in particular to a novel mold configuration that provides consistent shaping of glass sheets.
Shaped and tempered glass sheets are widely used as side windows or rear windows in vehicles such as automobiles and the like. To be suitable for such applications, flat glass sheets must be shaped to precisely define curvatures dictated by the shape and outline of the frames defined in the window openings into which the glass side or rear windows are installed. It is also important that the rear or side windows meet stringent optical requirements and that the windows be free of optical defects and reflective distortion that would tend to interfere with a clear viewing therethrough in their viewing area. Commercial production of shaped glass sheets for such purposes commonly include heating flat sheets to their heat softening temperature, shaping the heated glass to a desired curvature and cooling the sheets in a controlled manner to a temperature below the annealing range of the glass, to increase the resistance of the glass to breakage. During such processing, a glass sheet is generally conveyed along a substantially horizontal path through a tunnel-type furnace, heated to its heat softening temperature and transferred into a shaping station adjacent the furnace where a glass sheet is shaped. After shaping, the glass sheet is transferred to a cooling station where it is controllably cooled. The heat-softened glass sheet may be shaped using the variety of bending techniques, which are well known in the art. For example, in U.S. Pat. No. 4,662,925, heat-softened glass sheets are shaped between full surface upper and lower molds. In U.S. Pat. No. 4,830,650, the lower mold is a continuous flexible ring-type mold. In U.S. Pat. Nos., 4,272,274 and 4,518,411, the lower mold includes a number of transversely extending shaping lands with conveying rolls positioned between each land.
Using the shaping equipment disclosed in these prior art patents may present several problems. For example, using full surface upper and lower shaping molds increases the probability of marking the major surfaces of the shaped glass sheet. In configurations where the lower pressing surface is a segmented or continuous bent metal rail supported from an underlying support structure, e.g. an adjustable support post, there is the problem of providing a contoured surface that precisely matches the corresponding portions of the upper shaping mold. Furthermore, the configuration of the bent metal shaping rail must be continually monitored and readjusted as required to maintain the proper contour of the shaping rail throughout the glass sheet shaping campaign. In pressing configurations which include pressing lands, there is an increased possibility of marking the interior surface portions of the glass sheet due to contact with the shaping lands.
It would be beneficial to the glass sheet shaping art to provide a shaping arrangement which does not require continuous adjustment and realignment of the heat shaping surfaces and provides a consistent shaping of the glass sheets from part to part.